The head-up display device is mounted on, for example, a vehicle, and superimposes and displays various kinds of information on a scenery (foreground) ahead of a line of sight of a driver). The driver can visually recognize information necessary for driving while keeping the line of sight on a road surface or an object in a front direction. Such an on-vehicle head-up display device is known from Patent Literature 1.
A head-up display device known in Patent Literature 1 includes a display device that emits display light upward, a first mirror that reflects the display light emitted from the display device in a horizontal direction, and a second mirror that further reflects the display light reflected by the first mirror toward a windshield. The display is arranged under the second mirror. A driver can see the display light (displayed image) reflected on the windshield and recognize it as a scenery ahead of the vehicle, that is a virtual image that can be seen with the foreground.
In the head-up display device known in the Patent Literature 1, the display device and the first mirror become large-sized, and an optical path to be emitted from the first mirror to the second mirror becomes large, and the second mirror becomes large accordingly.
In addition, in a dashboard where the head-up display device is disposed, various other parts such as a duct and a harness are arranged, so the dashboard is fairly narrow. In order to arrange the head-up display device in such a narrow arrangement space without interfering with other parts, it is necessary to further downsize this head-up display device.